How many carbs per hour in a marathon: a practical guide

For a marathon, the sources point to about 30–60 g of carbohydrate per hour once you have been running between 1 and 2.5 hours, and up to about 90 g per hour for longer events (Jeukendrup, 2014). Those are ranges, not prescriptions. You find your number by rehearsing it on long runs, well before race day.

Your finish time decides which range applies

Jeukendrup (2014) scales carbohydrate advice with duration. Small amounts are enough for about an hour. Between 1 and 2.5 hours the range is around 30–60 g per hour. For longer events it rises to about 90 g per hour, and only when the carbohydrate comes from multiple transportable carbohydrates, which is a reason to read the label on a product before you buy twenty of them.

Duration is the lever. A runner finishing in 2 hours 30 minutes sits at the top edge of the middle band. A runner finishing in 4 hours 30 minutes spends the last two hours of the race beyond 2.5 hours, so the longer-event guidance applies to them.

Treat 90 g per hour as a ceiling, not a goal. The same source says the gut can be trained to tolerate more, so a number that works for another runner may not work for you today. If you have never fuelled in training, start at the low end of the middle band.

Turn grams per hour into a clock you can follow

Grams per hour are useless at kilometre 25. A timer is not. Take a hypothetical runner who expects to finish in 4 hours 30 minutes and aims for 40 g per hour, the lower half of the 30–60 g band. Over 4.5 hours that is 180 g. With gels that carry 20 g each (an example size, so check the label on yours), that is one gel every 30 minutes and nine in total.

Aiming for 60 g per hour changes the arithmetic: 20 g every 20 minutes, 270 g over 4.5 hours, 13 to 14 gels. That is a lot of packets to carry and open at pace. It is a good reason to settle the number in training, not in the race.

The common mistake is fuelling by feel. Runners wait until they feel flat, then take two gels together, an amount the stomach has never seen in training. Fuel on the clock, in equal portions, and the amounts stay comparable from one long run to the next.

Rehearse the plan on your long runs

Thomas, Erdman and Burke (2016) wrote a joint position statement for the ACSM, the Academy of Nutrition and Dietetics and Dietitians of Canada. It says fuel intake before, during and after endurance exercise should be planned and practised, and that individual tolerance varies. Jeukendrup (2014) adds that the gut can be trained to tolerate more. Both point to the same place: the long run.

Keep that run easy. Our guide to the long run: how far, how slow and how often explains why. Fuel practice does not change the pace. A short piece at marathon pace late in a marathon block can test fuel at race effort, once easy long runs are already a habit.

Here is one reasonable way to build up. On long runs of 90 minutes or more, start at 30 g per hour. If your stomach stays quiet, add about 10 g per hour every second or third long run, until you reach the amount you plan to use on race day. If it does not stay quiet, go back to the last amount that worked and hold it for another run or two. This is one option, not a rule.

Use the products you will use in the race. Look up what the organisers hand out on the course and practise with those too. Fuel, shoes and pacing are all race-day routines, and all of them belong in training first. Runapt's marathon plans include a weekly long run that builds towards race day, so the rehearsal slot is already in the week.

Decide in advance what to do when it goes wrong

A rule written before the race beats a decision made at kilometre 30. Three cover most cases:

Stomach unsettled in training: drop to the previous amount for the next long run. Do not stop fuelling altogether.
A gel missed: take the next one at its scheduled time. Do not double up.
An unfamiliar product on the course: skip it and carry your own.

A pace you can hold steadily also keeps the schedule simple. Check your target against the marathon pace chart, and set paces from a recent race or time trial, not from a goal time.

Stomach trouble that keeps coming back, dizziness or chest symptoms are not a fuelling question. See a doctor or physio.

What to do this week

Estimate your finish time and pick the band: 30–60 g per hour up to 2.5 hours, and a higher range only for longer events.
Multiply grams per hour by hours. At 40 g per hour for 4.5 hours that is 180 g.
Divide by the carbohydrate in one portion of your product to get the number of portions and the minutes between them.
On this weekend's long run, fuel on a timer, starting at 30 g per hour.
Write down how your stomach felt, then choose next week's amount: the same, a little more or a step back.

If you want long runs that build towards race day, start a marathon plan in Runapt. The first marathon training plan guide below covers the weeks around those long runs.

FAQ

How many carbs per hour do you need in a marathon?

Jeukendrup (2014) gives about 30–60 g per hour for efforts of 1 to 2.5 hours and up to about 90 g per hour for longer events. Start at the low end and build up on long runs. Tolerance varies, so your number is the one you have practised.

How many gels do you need for a marathon?

It depends on your finish time and the carbohydrate in each gel. As an example, a runner finishing in 4 hours 30 minutes at 40 g per hour needs 180 g, which is nine gels of 20 g. Divide your own total by the number on the label.

Can you train your stomach to take more carbs?

According to Jeukendrup (2014), the gut can be trained to tolerate more. In practice that means raising the amount in small steps on long runs, not trying a bigger number on race day.

Should you use the same fuel in the race as in training?

Yes. Thomas, Erdman and Burke (2016) say fuel intake should be planned and practised, and that individual tolerance varies. Find out what is on the course and rehearse with it, or carry your own. The first marathon training plan guide shows where those rehearsals fit.

Sources

Jeukendrup, A. (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine, 44(Suppl 1), S25–S33. https://doi.org/10.1007/s40279-014-0148-z

Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). Nutrition and athletic performance. Medicine & Science in Sports & Exercise, 48(3), 543–568. https://doi.org/10.1249/MSS.0000000000000852